Dikegulac, its salts, and related derivatives are well known in the art to be useful as plant growth regulators and/or herbicides. Methods for the preparation of dikegulac, its salts, and related derivatives are described in, for example, U.S. Pat. No. 3,832,355 to Jaffe et al; U.S. Pat. No. 4,007,206 to Szkrybalo, U.S. Pat. No. 4,337,080 to Szkrybalo, and U.S. Pat. No. 5,688,971 to Kwiatkowski et al.
The present invention relates to a novel method for the preparation of dikegulac, its salts and related derivatives, from 2-Keto-L-gulonic acid. 2-Keto-L-gulonic acid is an important, well known and readily available intermediate in the manufacture and production of vitamin C. It is derived from sorbitol which is first oxidized to L-sorbose by bacteria. The L-sorbose is then subjected to condensation with acetone in the presence of sulfuric acid followed by oxidation with permanganate and hydrolysis of the diisopropylidene derivative (dikegulac) by boiling in the presence of an acid. This procedure is described in, for example, U.S. Pat. No. 2,301,811 to Reichstein. Also, much more efficient and cost effective processes to directly produce 2-Keto-L-gulonic acid are known. They do not involve its diisopropylidene derivative (dikegulac) as an intermediate. Biochemical oxidation using Pseudomonas is described in U.S. Pat. No. 3,043,749 to Huang while biochemical oxidation using Pseudomonas and Acetobacter is described in U.S. Pat. No. 3,234,105 to Motizuki, et al.
In the prior art, it has also been known to prepare dikegulac, its salts, and related derivatives by the treatment of 2-Keto-L-gulonic acid with 2,2-dimethoxypropane, (see U.S. Pat. No. 5,688,971 to Kwiatkowski et al.). However, the process uses a number of filtration, trituration, and drying steps which increase the time and cost needed to prepare the final product. In addition, the process of the prior art Kwiatkowski et al. patent uses large volumes of solvents. Although the prior art Kwiatkowski et al. process provided an improved approach for the preparation of dikegulac, the process described is still not as cost effective as it could be.